Bulk acoustic wave resonator with ceramic substrate

Abstract

A bulk acoustic wave resonator is disclosed. The bulk acoustic wave resonator can include a ceramic substrate, and a piezoelectric layer on the ceramic substrate. The bulk acoustic wave resonator can also include first and second electrodes positioned on opposing sides of the piezoelectric layer. The bulk acoustic wave resonator can also include passivation layers that includes a first passivation layer and a second passivation layer. The first passivation layer can be positioned between the ceramic substrate and the first electrode. The second electrode can be positioned between the piezoelectric layer and the second passivation layer. The bulk acoustic wave resonator can further include a frame structure along an edge of an active region of the bulk acoustic wave resonator.

What is claimed is: 
     
       1. A bulk acoustic wave resonator comprising:
 a ceramic substrate, the ceramic substrate being a spinel substrate having an air cavity etched therein; 
 a piezoelectric layer above the ceramic substrate; 
 first and second electrodes on opposing sides of the piezoelectric layer; 
 passivation layers including a first passivation layer and a second passivation layer, the first passivation layer covers the air cavity etched in the spinel substrate and is positioned between the ceramic substrate and the first electrode, and the second electrode being positioned between the piezoelectric layer and the second passivation layer; and 
 a frame structure along an edge of an active region of the bulk acoustic wave resonator. 
 
     
     
       2. The bulk acoustic wave resonator of  claim 1  wherein the ceramic substrate is a magnesium aluminate (MgAl 2 O 4 ) spinel substrate. 
     
     
       3. The bulk acoustic wave resonator of  claim 1  further comprising a surface acoustic device disposed in the air cavity. 
     
     
       4. The bulk acoustic wave resonator of  claim 3  wherein the air cavity is formed to have an acute angle with respect to the surface of the ceramic substrate. 
     
     
       5. The bulk acoustic wave resonator of  claim 1  wherein the bulk acoustic wave resonator is a film bulk acoustic wave resonator. 
     
     
       6. The bulk acoustic wave resonator of  claim 1  further comprising an acoustic mirror positioned between the ceramic substrate and the first electrode. 
     
     
       7. The bulk acoustic wave resonator of  claim 1  further comprising an acoustic mirror positioned on two laterally spaced sides of the ceramic substrate beneath the frame structure. 
     
     
       8. The bulk acoustic wave resonator of  claim 1  wherein the ceramic substrate includes a planarized surface facing a center portion of the piezoelectric layer, the planarized surface having a roughness of less than 3 nanometers. 
     
     
       9. The bulk acoustic wave resonator of  claim 1  wherein the ceramic substrate is a polycrystalline spinel substrate having a density within a range of 3.4 to 3.7 grams per centimeters cubed. 
     
     
       10. The bulk acoustic wave resonator of  claim 1  wherein at least a portion of the second electrode has a different thickness than the first electrode. 
     
     
       11. The bulk acoustic wave resonator of  claim 1  wherein the frame structure includes a raised frame structure. 
     
     
       12. The bulk acoustic wave resonator of  claim 1  wherein the frame structure includes a raised frame structure and a recessed frame structure. 
     
     
       13. The bulk acoustic wave resonator of  claim 1  wherein the frame structure includes a first raised frame layer, and a second raised frame layer positioned between the first electrode and the piezoelectric layer. 
     
     
       14. An acoustic wave filter comprising:
 a bulk acoustic wave resonator including a piezoelectric layer on a ceramic substrate being a spinel substrate having at least one cavity etched therein, first and second electrodes on opposing sides of the piezoelectric layer, a first passivation layer that covers an air cavity etched in the spinel substrate and is passivation layer positioned such that the second electrode is positioned between the piezoelectric layer and the second passivation layer, and a frame structure along an edge of an active region of the bulk acoustic wave resonator, the ceramic substrate being a spinel substrate; and 
 a plurality of acoustic wave resonators, the bulk acoustic wave resonator and the plurality of acoustic wave resonators together arranged to filter a radio frequency signal. 
 
     
     
       15. The acoustic wave filter of  claim 14  wherein the ceramic substrate is a magnesium aluminate (MgAl 2 O 4 ) spinel substrate. 
     
     
       16. The acoustic wave filter of  claim 14  wherein the radio frequency signal has a frequency in a range from 5 gigahertz to 10 gigahertz. 
     
     
       17. A packaged module comprising:
 a packaging substrate; 
 an acoustic wave filter on the packaging substrate and configured to filter a radio frequency signal, the acoustic wave filter including a bulk acoustic wave resonator, the bulk acoustic wave resonator including a ceramic substrate being a spinel substrate having an air cavity etched therein, an active region of the bulk acoustic wave resonator covers the air cavity etched in the spinel substrate, and a frame structure outside of a middle area of an active region of the bulk acoustic wave resonator; and 
 a radio frequency component on the packaging substrate, the acoustic wave filter and the radio frequency component being enclosed within a common package. 
 
     
     
       18. The packaged module of  claim 17  wherein the ceramic substrate is a magnesium aluminate (MgAl 2 O 4 ) spinel substrate. 
     
     
       19. The packaged module of  claim 17  wherein the radio frequency component includes a radio frequency switch. 
     
     
       20. The packaged module of  claim 17  further comprising a surface acoustic wave resonator disposed in the air cavity.